A large number of fish die, is it lack of oxygen?

The epidemic season of tilapia hemorrhagic disease is long, and the epidemic season is from June to September. At the time of onset, the water temperature was more than 25 ℃. The morbidity and mortality rate is high. During the epidemic, the morbidity can reach 50% Murray 70%. It is reported that the mortality rate can reach 30% Mui 90%, or even be wiped out. The types of disease can be divided into acute and chronic. Acute morbidity and death often occur within a week, and chronic morbidity lasts as long as two or three weeks or even two months. The disease can occur in a wide range of water areas, including pond culture and reservoir cage culture.

Symptoms: there are generally two types in practice, the first is mainly reflected in the redness of the body surface, which mostly occurs in the lower jaw, Gill cover, fin and other parts, some exophthalmos and intraocular congestion; dissection can find intestinal congestion, spleen, kidney, gallbladder enlargement, liver from normal reddish brown to tawny or grayish white. This kind of symptom can cause acute death, once the early treatment is not right, it will make the treatment more difficult. Another type is mainly characterized by local congestion in the operculum and body surface, sometimes around the orbit, abdominal enlargement, yellowish ascites in the abdominal cavity, light hepatomegaly, enlargement of kidney and gallbladder, and intestinal congestion. It is different from the typical symptoms of streptococci, such as exophthalmos, hyperemia around the eyeballs, redness or severe bleeding on the inside of the operculum. Causes of the disease: in recent years, the stocking density and culture yield of tilapia have increased greatly; the water quality of the pond has deteriorated seriously, the sediment has aged, and the water quality has not been adjusted in time during the growing season (some places can not even change water all the year round). The contents of ammonia nitrogen and nitrite in pond water seriously exceeded the standard, resulting in the aging of pond water and the proliferation of pathogens in the water. Lack of necessary nutrients in feed, feeding deteriorated and bad feed in culture, resulting in organic lesions in liver, kidney and other organs, decreased body resistance, resulting in secondary bacterial infection; some farmers did not prescribe the right medicine to the case, misuse pesticides and pesticides, etc. In addition, the long-term inbreeding of tilapia leads to the serious degradation of its excellent genetic traits, or the degree of purification and rejuvenation of hybrid tilapia parents is not enough, resulting in insufficient male rate and germplasm degradation of their offspring hybrid lines of tilapia. and germplasm degradation is bound to weaken disease resistance; in addition, the oneness of pond-cultured varieties is also one of the reasons for the outbreak of the same disease every year.

Prevention: it is recommended that the stocking density is appropriate, and appropriate amount of silver carp and crucian carp are raised in order to remove the residual bait and regulate the water quality. Select high-quality and strong fish species, operate carefully to prevent fish body injury. Thoroughly clear the pond for disinfection, remove too much silt and transport it away from the breeding ground. Timely change of water, injection of new water, regulation of water quality and keeping water fresh can reduce the occurrence of fish disease. Pay attention to nutrition, feed to be hygienic, high quality, do not feed deteriorated feed, unclean feed. In the period when fish disease is easy to occur, drugs (such as Yuyuqing series) are used for regular prevention, and antibacterial drugs such as Yubikang and allicin are mixed into the feed to make bait.

Treatment: sprinkle the whole pool with 200-250ml/ mu of rice, once a day, twice a day. If the water quality is poor or pesticides have been indiscriminately used at the time of the disease, and those that lead to a decline in food intake can be sprinkled with pond jiedu bao series first, stabilize and then disinfect again. Pay attention to feeding oxytetracycline 0.3-0.5%, appetizer detoxification powder 0.4%, Baogantai 0.5%, and sodium cholate if ascites occurs. In addition, sulfadiazine is also fed in production, and the effect is remarkable.